Electromigration is the transport of material caused by the movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. A conductor, such as a wire line or interconnect in an IC, is especially susceptible to electromigration when current densities through the conductor are relatively high. Electromigration decreases the reliability of ICs because it may result in voids (i.e., open circuit) and/or shorts along conductive paths within the IC, which may ultimately cause the IC to fail. As IC dimensions continue to decrease in size, electromigration increases in effect and significance.
In-rush current is the maximum, instantaneous input current drawn by an electrical device or circuit when turned ON or otherwise activated in some way. For dynamically saving power, clock-gating is widely used on modern ICs. Consequently however, in-rush current issues result when large currents flow into a circuit when the clock-gating is turned OFF, which may cause considerable IR-voltage drop. The resulting IR-voltage drop may cause operational status changes in transistors, such as turning ON a transistor that is supposed to be OFF. Moreover, in-rush current issues are typical near power switches of the IC, which often makes it a location specific issue. However, chip area at such locations may be very limited due to the IC's design, and thus the amount of chip area occupied by a proposed solution to the in-rush current issue should be as small as possible.
Jitter is the frequency deviation from the static periodicity of a periodic signal. The sources of jitter include power supply noise, data path noise, phase distortion on the circuit (e.g., caused by phase-lock-loops), etc. Jitter can be quite problematic for ICs related to many different applications.
Very commonly, ICs of the prior art employ decoupling capacitors (e.g., “de-caps”) to mitigate the above undesirable effects of electromigration. IR-voltage drop caused by in-rush currents, and jitter. Specifically, de-caps are inserted at strategic points in a circuit where one or more of the above problems are anticipated. However, de-caps have distinct drawbacks. First, they consume large chip areas, which in some locations of the IC (e.g., near a power switch) makes their use very impractical or difficult. Second, some de-caps consume significant power since they may include one or more transistors. Third, de-caps have a frequency derived impedance that is selected based on the anticipated operating frequency of the circuit. Problematically, changes to the operating frequency of the circuit (e.g., when the IC enters a lower power state) may negatively affect the performance of the de-cap, which may have to be re-tuned to re-optimize performance.
There is a need for methods and devices that mitigate the problems associated with electromigration, in-rush current based IR-voltage drop, and jitter that consume less power, consume less chip area, and are robust to changes in the operating frequency of the IC.